1. Field of the Invention
This invention relates to test apparatus for probing electronic circuit boards, and more particularly, to test apparatus for simultaneously probing both sides of a fine pitch electronic circuit board.
2. Background Information
Test procedures applied to fine-pitch electronic circuit boards, such as multi-chip modules and multi-layer ceramic substrates, include bringing one or more probes into physical contact with individual circuits on the board. This is typically done using a cluster prober with a number of simultaneously engaged probe contacts in a fixed relationship, or using a serial prober moving one or more independent probes in a data driven fashion using map data. The cluster prober less flexible and requires a large capital investment for a custom probe head for each product type. While a serial prober can position probes to handle a variety of products easily, the use of such a device for highly dense circuit boards requires additional time. Since a large number of circuits must be checked in a dense board, the probe must move rapidly between test points. Probing should be done as quickly as possible to minimize the number of testers required to handle the output of a manufacturing line.
Probing at high speeds puts special demands on the probing system. Since the features to be probed are very small, great accuracy is required of the probing system. If the system structure vibrates excessively due to the acceleration forces which must be applied to move the various stages of the prober, the accuracy of the system may be affected. Furthermore, the product being tested may be damaged if the probe tip continues to vibrate during the test. Because of the high operational speeds and usage rates of this type of test equipment, an ability to perform maintenance operations rapidly and efficiently is an important factor in reducing operating costs of the test process and in increasing the availability of the test equipment. An important example of the type of maintenance which must be performed frequently is the replacement of probe tips.
Since complex circuits typically extend along both sides of a fine-pitch electronic circuit board, the ability to probe both sides of the board rapidly, accurately, and simultaneously is becoming increasingly important. While systems capable of probing both sides of the circuit board are becoming available, a particular need exists for a probing system which can probe both sides of the circuit board being tested, while providing the flexibility of a serial prober, while facilitating the installation and removal of circuit boards to be tested, and while providing physical access to the probing system for maintenance functions.